Recording and reproduction of electrical impulses



Jilly 1940' E. w. KELLOGG RECORDING AND REPRODUCTION OF ELECTRICAL IMPULSES Filed March 31, 1939 2 Sheets-Sheet l lnnentor W K e llo 29 Edward Gnomeg y 9, 0- E. w. KELLOGG 2,206,963

RECORDING AND REPRODUGTI ON OF ELECTRICAL IMPULSES Filed March 51, 1939 2 Sheets-Sheet 2 luventor Edward W, Kellogg Cnorneg Patented July 9, 1940 RECORDING AND REPRODUCTION OF ELECTRICAL IBIPULSES" Edward W. Kellogg, Moorestown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 31, 1939, Serial No. 265,271

Claims. (01. 1'79100.3)

This invention relates to the photographic revention to a combined galvanometer and a light cording and reproduction of electrical impulses valve recorder, and such as those of audio frequency, and has for its Figure 4 illustrates the application of the inprincipal object the provision of an improved apvention to a multi-galvanometer type of re 5 paratus and method of operation whereby differcorder.

ent frequency components of said impulses are Fig. 1 illustrates the positive of a composite recorded in such different forms as are required to photographic record wherein a pair of variable obviate the distortion ordinarily involved in rearea push-pull record tracks Id and H are sepacording all the impulse frequencies in the same rated by a line or narrow opaque band 12, and a form, pair of variable density push-pull record tracks 10 It is known that the variable density type of i3 and I 4 are located in the normally clear por photographic record is relatively less distorted in 0 0 5 of the record tracks l0 and i I. In this recthe high frequency range and that the variable 0rd, the lower frequency components of the rearea type of record has certain advantages in the corded impulses are represented by the variable 15 low frequency range. Thus, in the case of the area push-pull track iD-H and'the higher fre- 15 variable area record, the limited resolving power quency impulses are represented by the variable of photographic film causes the valleys of the high density p sh-pull track l3! 4.. It is, of course, frequency waves to be filled in or' fogged, and apparent that any suitable means may be prothe high frequency peaks to be underexposed. vided for Sepa at these d fi frequency 2;), Due to the loss of transmission in the valleys, the components of the recorded impulses. Since such amplitude of the recorded waves is decreased and frequency Separating ans or filter networks are the high frequencies are attenuated. Ihis reduc- Well known to 611086 Skilled in the art, they have tion in average transmission results in extraneous not been illustrated in connection with the varisounds, the frequencies of which depend upon the ous illustrated embodiments of the invention.

envelope of the recorded high frequency compo- Fig. 2 ill s ra s an embodimen f h inv n- 25 nents. A low frequency variable area record, tion wherein light from a source I5 is projected however, has the advantage that it is less disthrough a lens a mu t -apertured mask H, a torted by the development or processing of the single-apertured s a cyli drical lens l9 photographic film. and a spherical lens 20 to a galvanometer mir- A further object of t i ti i t proror 2|. From this mirror, light is reflected 30 vide an improved sound record,whereby the above through a e the light slit of a mask 23 types of distortion are avoided. To this end, the a a lens 24 130 a D aP C record 25. relatively high frequency components of the The function of the multi-apertured mask. ll is sound are recorded by the variable density produce at the mirror 21 a pail 0f pp s te y method and the relatively low frequency com- Shaded Penumbra Shad-0W5 the images of Which ponents are recorded by t variame area ware vibrated transversely of the light slit 25 in ac-- od. More specifically, the lower frequencies are Cordance With the g frequency comh t recorded in the form of a push-pull variable area Thus the aperture 27 p duc s at the slit 23 an record and the higher frequencies are recorded in image Which is brightest at its lower ge and w the form of a variable density record which occubecomes gradually a e as its upper edge is ap- 410 pies the normally clear part of the variablearea proached- Similarly, the aperture 23 produces at c rd As 111 appear, t (jomposite the slit 26 an image 28' which is brightest at its has the important advantage that it may be upper edge and becomes ual y da ker as its played or reproduced by any usual type of ushlower edge is approached. If the operating coil pull reproducer, such as that disclosed byjUnited 29 f the recording a tcr is energizedst t t t 2,094,737, for l in accordance with the high frequency impulses, The invention will be better understood from as previously indicated, there is p oduced on the the following description when considered in conc d s p 25 a h frequency push-pull recnection with the accompanying drawings, and its track |3|4 Such as is shown in 1.

5o scope is indicated by the appended claims. The low frequency D- p T600111 track Referring to the drawings, |0| l is produced by the single-apertured mask Figure 1 illustrates the improved type of record, l8 which is moved longitudinally of the slit 26 Figure 2 illustrates the application of the inby means of operating coils 30 and 3%.. These vention to a penumbra type of impulse recorder, coils are supplied with the low frequency compo- Figure 3 illustrates the application of the innents'of the recorded impulses, and the distortion otherwise produced by fogging of the valleys and underexposing the peaks of the high frequency waves is not present in such low frequency waves. At the same time, the superiority of the variable area record track with respect to photographic development processes is to a considerable extent retained, i. e., distortion due to operation in the non-linear ranges of the H. and D. curve is largely avoided.

It should be understood that the masks I! and it are mounted closely together, only so much separation being provided as is necessary for mechanical reasons, that the function of the cylindrical lens i9 is to sharply focus in the plane of mask 23 the vertical edges of the aperture in mask l8 and of apertures 2'5 and 23 in mask l1, thus producing images tit-28 having sharp vertical edges. The apertures I! and I8 are slightly spaced from one another horizontally for the purpose of separating the images 21' and 28' and producing the image separation line or band l2 of Fig. 1.

Fig. 3 illustrates a modification wherein the variable area low frequency recording is effected by means of a galvanometer and the variable density high frequency recording is effected by means of a light-valve. Thus light is projected from the source I5 through the lens IS, a fixed single-aperture mask 32 and a lens 33 to the re cording galvanometer mirror 2i. From this mirror, an image 3 1 of the aperture in the mask 32 is reflected through the lens to the light slit mask 23. By means of the galvanometer 2i, this image M is vibrated longitudinally of the light slits 35 and 3B of the mask 23 and functions to produce on the record 25 a variable area record similar to the record l0--H of Fig. 1.

Mounted adjacent to the mask 23 is a threeribbon light valve 3l3839 to which the high frequency components of the recorded impulses are sup-plied through the leads 4!] and H. The use of a three-ribbon light valve in this manner to produce a variable density push-pull sound track is well known. If the opening between the ribbons 3'? and 38 is aligned with the light slit and the opening between the ribbons 38 and is aligned with the light slit 35, as illustrated, it necessarily follows that the light transmitted through the slits S5 and 36 is modulated by the impulses applied to the terminals M3 and M. Thus, when current flows between the terminals it and ii in one direction, the spacing between the ribbons ill and 38 becomes narrower and that between the ribbons 38 and 39 becomes wider. When the direction of current flow is reversed, the spacing between the ribbons is changed in the opposite manner.

In order that the positive and negative parts of the variable density push-pull records may be recorded directly opposite each other, and thereby suitable for reproduction on a standard push-pull reproducing system, there is provided between the light valve and the record 25 suitable refracting members 42 and 43. These members are so mounted in diiferent angular positions that the portion of push-pull record recorded through the slit 35 is displaced upwardly longitudinally of the record 25, and the portion recorded through the slit 36 is displaced in the opposite direction, thus bringing these two variable density records into the desired lBQ-degree phase relationship when scanned or reproduced by means of a single line of light. It is, of

course, apparent that the use of these refractors may be avoided if the light valve is replaced by light Wedges, in which case the two light slits 35 and 36 may be horizontally aligned with one another.

The modification of Fig. 4 differs from those of the previous figures in that both the high and low frequency recording elements are of the galvanorneter type. In this embodiment, light from the source I5 is projected through a lens M, the single-apertured mask 32 and a lens 55 to the horizontally vibratable mirror of the low frei quency variable recording galvanometer In terposed between the mirror of galvanometer it and that of the high frequency variable density galvanometer 2| are the lens in, the multi-apertured penumbra mask ll, the cylindrical lens l9 and the lens 20.

So much of the penumbra mask apertures 27 and 28 as are illuminated by the image it of the aperture in mask 32 are imaged at the light slits 46 and 41 in the form of penumbra shadows 2'! and 28. As explained in connection with Fig. l, the vertical edges of the images 2i" and 28 are sharply focused by the cylindrical lens l9, and the two images are darkest at their nearest horizontal edges and become gradually brigh: er as their offset horizontal edges are approached. These images having oppositely graded light intensities, and which move vertically in response to currents supplied to the galvanometer i, function to produce a variable density push-pull rccn at 0rd in exactly the same manner as is now employed and is described in U. S. Patent No. 2,095,318 to G. L. Dimmick.

When the operating coil of the variable area low frequency recording galvanometer is supplied with the low frequency components of the impulses to be recorded, the image 43 which consists in a highly illuminated rectangle, is vibrated by the mirror 46 horizontally with respect to the penumbra apertures 21 and 23 in mask plate L H, and the movements of the illuminated area have the same effect on the images 2i and 28 as the horizontal movements of the aperture in the plate l8 of Fig. 1, and there is produced on the record 25 variable area push-pull sound tracks separated by a distance determined by the separation of the slits 46 and 41. When the operating coil of the variable density high frequency recording galvanometer is supplied with the high frequency components of the impulses to be recorded, the penumbra images 21 and 28' are vibrated transversely of the slits 45 and A l by the mirror 2| and there is produced in the normally clear part of the low frequency variable area record a variable density record of the high frequency components of the recorded impulses.

It would not be feasible to apply to the recording system, as so far disclosed, the usual methods of ground noise reduction because darkening the variable density tracks as is commonly done in present variable density systems and which does not reduce the output of the variable density track would reduce the output the variable area tracks. It is possible, however, to compensate for the darkening of the track by increasing the amplitude of the light modulation in recording, in the manner described in my U. S. Patent No. 2,064,665. If this expedient is applied to the present invention, the darkening of the variable density track, as for example by biasing the light valve of Fig. would be compensated by increasing the modulation of the low frequency Variable area track. Alternatively, ground noise reduction might be obtained by narrowing the relatively transparent area allot-ted to the variable density recording, and compensating for the reduced output from the variable density recording, which this narrowing would produce, by increasing the amplitude with which said variabe density track is recorded. The narrowing of the relatively transparent area might be obtained by moving shutter vanes as is now done in making variable width recordings.

It is apparent that the present invention is not restricted to the particular types of recorders herein disclosed, but is readily applicable to various other types of apparatus in view of this disclosure.

I claim as my invention:

1. The electrical impulse recording method which includes separating the high and low frequency components of said impulses, recording said low frequency components as a variable area record track, and recording said high frequency components as a variable density record track located in the otherwise transparent part of said variable area sound track.

2. The electrical impulse recording method which includes segregating the frequencies of said impulses in different groups, recording one of said frequency groups as a push-pull variable area record track, and recording another of said frequency groups as a push-pull variable density record track located in the otherwise clear part of said variable area record track.

3. The electrical impulse recording method which includes separating the high and low frequency components of said impulses, recording said low frequency components as a push-pull variable area record track, and recording said high frequency impulses as a variable density record track located in the otherwise transparent part of said variable area record track.

4. A composite electrical impulse record whereon the low frequency components of said impulses are recorded as a push-pull variable area record track, and the high frequency components of said impulses are recorded as a push-pull variable density record track located in the otherwise clear part of said variable area record track.

5. A composite electrical impulse record whereon the low frequency components of said impulses are recorded as a variable area record track, and the high frequency components of said impulses are recorded as a variable density record track located in the otherwise clear part of said variable area record track.

EDWARD W. KELLOGG.

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